It is known for the fuselage of an aircraft to comprise a structure, the principal function of which is to transmit forces, onto which structure is attached a shell which gives the aircraft its aerodynamic properties. Thus, in flight, air flows along the outside face of the fuselage.
The structure comprises an assembly of beams, frames, stringers, stiffeners or other components. These elements can be made of metal and/or of composite materials. In parallel, the shell takes the form of a juxtaposition of panels or complete sections of metal plates connected to the structure by riveting or by any appropriate means. As a variant, these panels may be made of composite materials.
FIGS. 1 and 2 show an aircraft 10 and various zones such as a forward landing gear bay 12, inside which the forward landing gear 12 is designed to be housed when in flight, a forward technical bay 14, inside which electrical equipment and systems 16 are arranged, followed by what is known as a cargo hold 18. The forward landing gear bay 12 and the technical bay 14 are arranged in the nose section of the aircraft underneath the cockpit. In the case of an airplane intended for carrying passengers, the cargo hold 18 is arranged underneath the passenger cabin.
Certain zones of the aircraft are thermally insulated from the outside of the fuselage and are pressurized, such as the bay 14, the hold 18, the cockpit and the passenger cabin, while others, such as the forward landing gear bay 12, are not. The temperature of the air inside the landing gear bay can thus drop to −50° C. in flight, close to the temperature of the air outside the fuselage. The air inside said landing gear bay can be exposed to flows of speeds considerably lower than those of the air outside the fuselage.
The forward landing gear bay 12 is part of the structure of the aircraft and comprises two side walls 20. One of these is shown in section in FIG. 4 with a base linking the upper edges of the side walls and a front wall and a rear wall linking, respectively, the front and rear edges of the side walls. The frames of the structure of the aircraft, arranged at the level of the forward landing gear bay, do not extend all the way around the fuselage and comprise a cut-out through which the landing gear can move. These frames are thus connected to the lower edges of the side walls 20 of the landing gear bay. In order to transmit forces, the faces of the walls of the forward landing gear bay 12 comprise a plurality of reinforcing elements. Thus, as shown in FIG. 4, the outer face 22 of the side walls 20 comprises stiffeners 24 oriented substantially perpendicular to the planes of the frames.
According to another aspect, the aircraft comprises numerous elements such as electrical equipment and systems 16, present in the forward technical bay 14, which produce heat and must be cooled.
As shown schematically in FIG. 1, in the case of the electrical equipment and systems 16, air taken from the cargo hold 18 is blown into the electrical equipment and systems 16. This air, which heats up as it passes through the latter, is drawn off so as to be conveyed to one or more heat exchanger(s) 26. According to one configuration, a network of ducts 28 for the fresh air is provided between the cargo hold 18 and the electrical equipment and systems 16, and a network of ducts 30 for the heated air is provided between the electrical equipment and systems 16 and the heat exchanger 26.
As shown in FIG. 3, the heat exchangers 26 are arranged in a duct or ducts 32 through which flows air which is taken from outside the fuselage via at least one air intake 34 and which is rejected outside the fuselage via at least one air outlet 36.
Capturing the air via the intake 34 and rejecting it via the outlet 36 gives rise to aerodynamic perturbations which increase both the drag and the energy consumption of the aircraft. These perturbations must therefore be minimized.
However, aircraft cooling requirements are exhibiting a substantial upward trend. This increase in cooling requirements results in several drawbacks, specifically the increase in aerodynamic perturbations due to the increased volume of air taken and rejected, the increase in the on-board mass due to the increase in number and/or size both of the ducts 28, 30 and 32 and of the heat exchangers 26.
The shape and/or size of the intakes 34 and outlets 36 are optimized in order to limit the aerodynamic perturbations. For example, document FR-2.915.733 describes a movable outlet grating.
In order to limit these perturbations, other solutions have been developed for transferring the heat into the fuel tanks or into the engines by using the fuel as a heat transfer fluid. As an example, document FR-2.936.224 describes a system which makes possible for heat to be rejected via the engines. However, the heat absorption capacity of the fuel tanks or the engines is limited and is insufficient and inferior to the requirements of the aircraft.
In addition or as an alternative, other documents describe using the fuselage in order to dissipate heat. To this end, ducts are arranged close to the inner surface of the fuselage in order to transfer heat from the heat transfer fluid circulating in the ducts to the skin of the fuselage and then from the skin of the fuselage to the environment outside the aircraft. This solution is not entirely satisfactory as the efficiency of the heat transfer from the heat transfer fluid to the environment outside the aircraft depends on the efficiency of a first heat transfer from the heat transfer fluid to the skin of the fuselage and of a second heat transfer from the skin of the fuselage to the outside environment.
As the wall of the duct carrying the heat transfer fluid is not in direct contact with the outside environment, the transfer of heat is not optimal and depends, essentially, on the contact area between the walls of the ducts and the skin of the fuselage. Moreover, this heat transfer is also affected by the high-speed air flows outside the fuselage of the aircraft which can give rise to substantial heating due to the friction between the air and the fuselage.